The qua-quine starch (QQS) gene (locus ID At3g30720; GenBank Accession Nos. EU805808.1 and NM_113075.4) has been found to have an effect on plant biochemical components in Arabidopsis. The QQS gene encodes a protein that contains 59 amino acids, has no known function, has no sequence similarity to other proteins in Arabidopsis or other organisms, has no known catalytic motifs, and no known structural motifs. Analysis of the QQS promoter indicates that it has a CCA1 binding site motif (AAAAATCT) at position −734, a TGA1 binding site motif (TGACGTGG; bZip transcription factor function) at position −504, an UPRMOTIFIAT motif (TGACGTGG; unfold protein response) at position −504, an ABRE-like binding site motif (GACGTGGC; ABA function) at position −503, and an ACGTABREMPTIFA2OSEM motif (ACGTGGC; ABA function) at position −502. QQS RNA transcripts increase during pollen development (from uninucleate microspores to bicellular pollen to tricellular pollen to mature pollen) in WT (WT) Arabidopsis, reaching peak levels in mature pollen. In wild type (WT) Arabidopsis, activity of the QQS promoter as determined using the β-glucuronidase (GUS) gene reporter system is evident at 2 days after imbibition (DAI) in hypocotyls and root tips. As seedlings grow, QQS expression expands to the vasculature, mesophyll cells, hydathodes, and trichomes of leaf blades and petioles. Microscopic dissection indicates no expression is detected in shoot meristem; the dark GUS staining in the shoot tip is associated with the adjacent vasculature. GUS activity is higher in mature leaves compared to young emerging leaves; it consistently appears somewhat unevenly distributed, and is predominantly located in the vasculature; this pattern is maintained throughout development. QQS expression is low in flower buds; however, by flower opening QQS expression is evident in pedicels, sepals, filaments, mature pollen, stigma papillae and styles, but not in petals. During silique development, QQS expression rises in the stigma papillae and style, and becomes apparent throughout the maternal tissues of the silique wall and receptacle. QQS is expressed in roots throughout development. Expression is highest in the root tip, specifically the root cap, columella cells and peripheral cap, and to a lesser extent in the root meristem region, but not in the epidermis. QQS is expressed at the site of lateral root initiation, and in the root tip and vasculature during its emergence; as the lateral root matures, expression remains detectable throughout the root cortex vasculature. GUS activity driven by the QQS promoter was higher in the Atss3 (starch synthase 3) single mutant than in WT under virtually all conditions. Expression was detectable throughout the entire seedling at 2 DAI, as well as later in development, in particular in leaves, flowers and roots. Although the general pattern of expression is similar in the Atss3 mutant and WT, QQS is expressed ectopically in petals in the Atss3 mutant. QQS RNA accumulates neither in the nucleus nor in the plastids. Expression of QQS promoter-GUS in the Atss2/Atss3 double-mutant background was more nuanced, but was in general similar to or somewhat lower than that in WT throughout leaf development. QQS transcripts increased seven-fold during the diurnal cycle in the Atss3 mutant compared to WT Arabidopsis; QQS protein levels also increased in the Atss3 mutant compared to WT Arabidopsis. Analysis of QQS RNAi (interfering RNA) mutants showed that starch content increased 20-30% at the end of the light cycle (about the same increase as observed in Atss3 mutants) due to increased starch biosynthesis and not decreased starch degradation; there was no difference in starch content at the end of the dark cycle. Starch content decreased to WT level within four hours of the dark cycle. All of the above examples are described in Li et al., Plant Journal 58: 485-498 (2009).
QQS expression has been observed to be tightly linked with a variety of developmental, environmental, and genetic perturbations (see, e.g., Arendsee et al., Trends in Plant Sci doi:10.1016/j.tplants.2014.07.003 (2014); Li et al. (2009), supra; and Li et al., Plant Biotech J: 13(2): 177-187 (2015)). Its role, however, in such perturbations has not been elucidated. For example, PEN3 (Penetration Resistance 3 (At1g59870, PEN3, ABC binding cassette transporter gene) confers non-host resistance to fungal and oomycete pathogens. QQS has been reported to be the only gene that is up-regulated in pen3 knock-out (KO) mutants; however, QQS is up-regulated in infected and non-infected mutants (Stein et al., Plant Cell 18(3): 731-746 (2006)). As another example, two syntaxins, namely SYP121 (At3g11820, PEN1) and SYP122 (At3g52400) confer resistance to powdery mildews. Knock-outs of these genes result in increased sensitivity to these pathogens; QQS has been reported to be the only gene that is up-regulated in both (Zhang et al. (2008)). In contrast, while PEN3 and EXL1 are up-regulated following exposure to some pathogens, QQS is down-regulated in response to infection by some pathogens, such as Pseudomonas syringae (Kwon et al., Planta 236(3): 887-900 (2012); and Thilmony et al., Plant J. 46(1): 34-53 (2006)). When Arabidopsis plants were inoculated with Phytopthera infestans, QQS reportedly was first down-regulated at 6 hrs post-inoculation and then up-regulated at 12 and 24 hrs post-inoculation (Scheel et al., Experiment ID “E-GEOD-5616” in ArrayExpress).
In view of the foregoing, it is an object of the present disclosure to provide materials and a method for increasing a plant's resistance to a pathogen or a pest. More specifically, it is an object of the present disclosure to express Qua-Quine Starch (QQS) in a plant, which is at risk for infection with a pathogen or a pest and the wild-type of which does not otherwise express QQS, and selecting transgenic plants with increased resistance to the pathogen or the pest. This and other objects and advantages, as well as inventive features, will become apparent from the detailed description provided herein.